docs: def dv(self, orb):
          """Computation of the velocity increment in the reference frame of the orbit
  
          Args:
              orb (Orbit):
          Return:
              numpy.array: Velocity increment, length 3
          """
  
          orb = orb.copy(form="cartesian")
  
          if self.frame == "QSW":
              mat = to_qsw(orb).T
          elif self.frame == "TNW":
              mat = to_tnw(orb).T
          else:
              mat = np.identity(3)
  
          # velocity increment in the same reference frame as the orbit
          return mat @ self._dv